Small Flow Waste Treatment Systems

Treatment systems handling less than 1.0 million gallons per day are generally considered small treatment systems. For some packaged treatment systems, the principles of design are no different but the choice of equipment will usually differ from that used in large plants. This is usually due to the effect of economies of scale, whereby certain operations are economically feasible only on a large scale. In other cases, certain treatment systems such as septic tanks, Imhoff tanks, waterless toilets, mounding systems and composting toilets are only applicable to very small flows. Small packaged plants must make larger safety factor allowances for flow variation and temperature effects relative to total wastewater flows. Smaller package plants inherently have less operational flexibility; however, they are capable of performing effectively and efficiently. These small packaged plants may consist of trickling filter plants, rotating biological discs, physical-chemical plants, extended aeration activated sludge plants, and septic tanks. Design criteria for septic tanks, Imhoff tanks, waterless toilets, mounding systems, composting toilets, and filtration/reuse systems are given.